with classical Einstein tensor \(G_{\mu \nu }\)  (see e.g., [1]}),
but sourced by the expected value of the quantum stress-energy
tensor.The components of the quantum stress-energy tensor are
related in a simple manner to the ensemble quantities in
eqns.(REF ) and
(REF ). The derivation of the SCEE from an action
by Kibble and Randjbar-Daemi in [2]} makes this
relationship more precise. Such a theory of gravity has long been seen as a
desirable step intermediate to a full theory of QG, in part because it
contains well-established physics — QFTCS and classical GR
— in the limiting cases where they are valid. But there has been much debate
(see e.g., [3]}[4]}[5]}[6]}), on the other hand, as to the status of
semi-classical theories as true QG candidate; with many harboring a negative view. In the next chapter we conclude by tackling these criticisms head on, discussing what's good, what's bad, and what's ugly about the ED approach to semi-classical gravity.
